Big Block Cam LSA Thread

Several months ago on here there was a great discussion about narrow LSA cams in big blocks. I have searched a few times for it and can't find it. Does anyone remember it or have it bookmarked? Thanks!

If you know someone who responded to that thread, just search/view their posts.

Good idea, thank you.

LSA is just a byproduct of having the correct opening & closing points that YOUR engine & combo runs the best . there is A LOT more to it than just looking at the LSA of a cam

What's "narrow" to you? My Mini-Express is 107, in at 2 deg advanced.

That isn't narrow. I used to have an old super stock cam that was 102 and a buddy had a cam that was 99. They used to tighten up those lobes a bunch back in the day. Maybe someone still does.

I've ran and raced and dyno tune a bunch BB Mopar wedge motors with stock 440 size heads and narrow, tighter than 106 LSA, that all outran the other cars with similar parts with wider LSA and sometimes more lift and duration and than I had
I had one Reed Cam(solid flat tappet grind) that was suppose to been ground on a 104 LSA that was actually ground on a 101 LSA, I ended up installing it at 99 ATDC on the intake lobes and that rascal made the most HP and torque than many other cams with real similar lift and duration with wider LSA 108 ,110, 112 that I had used and tested The customer loved it saying it never quit pulling even above 7500 RPM Stock stroke 440 pump gas motor with a 850 CFM D.P. carb on a Eddy RPM intake and 906 heads

Wouldn't trying different LSA's be a way of determining what opening and closing points YOUR engine combo works best at.

The guys over at Bullet Racing Cams state that heavy cars need narrow lobe seps. They spec'd a cam for my 511 in a 3400# car as needed a 108. I recently found a Lunati shelf cam 276/284-.690 on a 106* lobe sep. Thought this might be good for a future build.

Here's a custom spec for a really heavy car:
5300 lbs Ramcharger 4wd
505 rb
TF 270
Auto with OD
5.13 gears, 37" tires.
Indy dual plane intake
10.2 :1.
If I was going to run Efi, they wanted to push the LSA 2 deg bigger.
This was chosen as a close to a dual purpose cam as I could get.
I need bottom end to move the truck as a street driver,but I also need HP for the wheel speed in the mud.

Who spec'd that for you? It doesn't have much duration thou, so should still make good torque i would think.

Bullet spec'd it from my info, most cams are ground for cars, or at the other end , towing with low compression ratio, so I though that was the safest way to go. I have lots of cylinder head so I can always go bigger if I need to.
They didn't think the valve train was going to be that successful over 5800 rpm so that's the ceiling for the motor.

Yeah, i was just curious who at Bullet.

Probabley the narrowest LSA needed would have been my first stroker. 535 cubes, 906 heads, 2.14 intake valves, probably didn't flow more than 260 cfm. I bet it would have liked a 98 lsa.
IMHO since the overlap cycle is often seeing five times the vacuum draw of max intake valve lift, getting the overlap correct and sufficient for the head flow is the most important event.
On the other hand my new mustang 5.0 4v has up to 130 lsa. Those 4v heads flow like crazy at low lift/overlap.

the overlap cycle is often seeing five times the vacuum draw of max intake valve lift
This^^^

LCA is a function of duration and overlap. Increased duration with the same LCA increases overlap. So If a given combination needs more duration then LCA has to widen to maintain the same overlap. Look at the LCA of big duration cams. It will be wider for most applications.
Doug

I've talked to so many people about all the parts for this build, I can't recall the guys first name.

I was taught early on many years ago that moving the LSA with no other changes would affect the power range of the motor just like advancing or retarding the cam. Wider LSA would loose bottom end with a higher HP peak RPM, moving them closer, tighter LSA, would make more power at the lower RPM range of that motor with no other changes

Two things that affect the amount of overlap versus duration are head efficiency and compression ratio. An 8/1 compression motor has to clear a lot more dead volume at overlap than a 16/1 motor. Also, as cam duration goes up beyond a certain point, on average the heads will be better and compression higher. I would bet that could be demostrated by looking at some stock class cams. If i am right, they should have a longer overlap period compared to total duration.

Most of the SB Mopar running well in NHRA stock use from 102 to 106 LSA installed from 2 to 6 degrees advanced on the ILC back many years ago when I was still talking to and helping some of those NHRA class racers